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Affecting on Brain Activation by Transcranial Direct Current Stimulation

Mohseni Salehi Monfared, Sadegh | 2014

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 45858 (05)
  4. University: Sharif University of Technology
  5. Department: Electrical Engineering
  6. Advisor(s): Vosoughi Vahdat, Bijan; Oghabian, Mohammad Ali
  7. Abstract:
  8. Transcranial direct current stimulation (tDCS) over the different brain regions has been documented in clinical and laboratory experiments. Anodal tDCS on the dorsolateral prefrontal cortex (DLPFC) has shown promising effects in enhancing cognition. Furthermore, such stimulations have been proposed in treatment of several neurological and psychological disorders. Investigations have verified the positive effect of such stimulations on drug addicts by diminishing their drug craving after stimulation. In spite of the extended research in this field, the effect of tDCS on different brain region and brain networks has yet not been studied through computational models. In this study, we evaluated the possible modulation effects of tDCS over the right DLPFC on the resting state networks (RSN), specifically default mode network (DMN) extracted based on functional magnetic resonance imaging (fMRI). The probable correlation between modulation in DMN and the immediate drug craving in abstinent methamphetamine users is also examined in this research. 19 methamphetamine abstinent users enrolled in the experiment after signing informed consent form approved by ethical committee of Tehran University of Medical Sciences. They were delivered DC stimulations. In this experiment, subjects were stimulated twice (wash out period was 1 week) through 20 minutes 2mA sham or active stimulationsThe anodal and cathodal electrodes were placed over the right DLPFC (F4 based on 10/20 system) and left DLPFC (F3) respectively. In each session, functional imaging (fMRI, 3.0T Siemens Tim Trio) was accomplished before and after receiving tDCS stimulations. Moreover, the subjects rated their immediate methamphetamine craving before and after stimulations by visual analogue scale (VAS) with a score range of 0 to 100, where 0 is "no craving" and 100 is "extreme craving". In order to extract DMN, 4D functional images were preprocessed by FSL 5.0.4. Afterwards, all the fMRI data were turned into a single 4D matrix by temporal concatenation. The components have been extracted using group independent component analysis (gICA) in Melodic software. The DMN component was distinguished and the following contrasts were tested using dual regression procedure: ((active > active baseline) > (sham > sham baseline)). Statistical evaluations showed no significant deference in the immediate craving comparing 2 sessions’ baseline (p>0.05). Thus, the significant decrease in drug craving after active stimulation compared to its baseline is attributable to tDCS’ effect (t= 3.25, df= 18, p < 0.05). Figure 2 illustrates the common DMN of all four fMRI sessions with a p<0.5 threshold, which includes Precuneus, the middle/superior temporal gyrus bilaterally, the middle frontal gyrus and Cingulate gyrus. Major modulation of DMN activity after active stimulation compared to sham is observed; modulated areas include the Precuneus, Posterior Cingulate cortex and right DLPFC. This study shows real tDCS on the right DLPFC lead to significant reconfigured DMN activity. We speculate these alterations may explain the decrease self-report craving in methamphetamine users after anodal stimulation. Given that changes in the intrinsic activity of brain networks of methamphetamine users can be obtained by tDCS, we can ensure this method have a robust effect on the treatment of the addiction
  9. Keywords:
  10. Functional Magnetic Resonance Imaging (FMRI) ; Brain Connectivity ; Transcranial Direct Current Stimulation (tDCS)

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